Conductive material, conductive paste, circuit board, and semiconductor device

ABSTRACT

A conductive material includes a first metal part whose main ingredient is a first metal; a second metal part formed on the first metal part and whose main ingredient is a second metal, the second metal having a melting point lower than a melting point of the first metal, which second metal can form a metallic compound with the first metal; and a third metal part whose main ingredient is a third metal, which third metal can make a eutectic reaction with the second metal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 12/850,950filed Aug. 5, 2010, which is a U.S. continuation application filed under35 USC 111(a) claiming benefit under 35 USC 120 and 365(c) of PCTapplication JP2008/054162, filed Mar. 7, 2008. The foregoing applicationis hereby incorporated herein by reference.

FIELD

The embodiments discussed herein are related to conductive materials,conductive pastes, circuit boards, and semiconductor devices.

BACKGROUND

It is required that a conductive material used for forming a conductivecircuit on a circuit board such as a printed wiring board or aninterlayer connecting between layers be chemically stable and have a lowelectric resistance. On the other hand, the circuit board such as theprinted wiring board where an electronic component is mounted isrequired to have a structure where conductive circuits are formed withhigh densities in a multi-layer manner. Accordingly, in recent years, aprinted wiring board where IVHs (Inner Via Holes) or blind via holes areformed with high density has been used. The IVHs or the blind via holesare formed by embedding the conductive materials in through holes or viaholes so that upper and lower layers are connected to each other. Withthis structure, it is possible to achieve high density mounting of theelectronic components.

As a method forming a conductive circuit on such a circuit board, asubtractive method has been used. In the subtractive method, a metalfilm as a conductive circuit is formed on an entire surface of theprinted wiring board and then unnecessary metal film is etched by usinga photolithography technique so that the conductive circuit is formed onthe circuit board. In addition, as another method of forming theconductive circuit on the circuit board, the following method has beensuggested for reducing the manufacturing cost. That is, a conductivepaste film including particles of a conductive material such as silver(Ag), copper (Cu) or carbon (C) and a binder dissolved by a solvent isprinted on the surface of the circuit board by a screen printing methodso that a circuit is formed.

In addition, the following method is also suggested. That is, the IVH orthe blind via hole is filled with a conductive paste and a curingprocess is applied so that a conductive circuit connects the interlayerof the circuit board.

Furthermore, a conductive material including plural particles having anelectrically conductive coating, where some of the particles are fusedto each other by the electrically conductive coating, has beensuggested. See Japanese Laid-open Patent Application Publication No.8-227613.

In addition, the following method has been suggested. That is, aconductive filler, where a film of tin (Sn) having a thickness of 1 μmis formed on surfaces of copper (Cu) particles by an electroless platingmethod, and a designated agent are mixed so that a conductive paste isformed. The conductive paste is printed by a screen printing method sothat a conductive circuit and via plugs are formed. See JapaneseLaid-open Patent Application Publication No. 2006-19306.

Furthermore, a conductive metal paste used for a terminal electrode of amonolithic ceramic electronic component has been suggested. See JapaneseLaid-open Patent Application Publication No. 2-46603. In this conductivemetal paste, an alloy formed of two kinds of metallic elements whosemelting point is lower than the melting points of the elements, and anintermetallic compound formed of the two kinds of the metallic elementshaving high melting points, are used. In this suggestion, a compoundmetal powder where zinc (Zn) is coated on a surface of a copper (Cu)powder is used as a terminal electrode of the monolithic ceramicelectronic component. By sintering at 500° C. through 600° C., diffusionprogresses between the zinc (Zn) and the copper (Cu) so that part of thepowder becomes brass and a high density sintered body is obtained. Inaddition, the remaining copper (Cu) is surrounded by the brass so thatoxidization of an electrode surface of the copper (Cu) terminal isprevented.

SUMMARY

According to an aspect of the embodiments, includes a conductivematerial including a first metal part whose main ingredient is a firstmetal; a second metal part formed on the first metal part and whose mainingredient is a second metal, the second metal having a melting pointlower than a melting point of the first metal, which second metal canform a metallic compound with the first metal; and a third metal partwhose main ingredient is a third metal, which third metal can make aeutectic reaction with the second metal.

Additional objects and advantages of the embodiments will be set forthin part in the description which follows, and in part will be obviousfrom the description, or may be learned by practice of the invention.The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe appended claims. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view for explaining embodiments;

FIG. 2 is a graph of temperature change and a measuring result of aheating amount by performing heating processes two times;

FIG. 3 is a view for explaining a second embodiment;

FIG. 4 is a view for explaining a third embodiment;

FIG. 5 is a view for explaining a fourth embodiment; and

FIG. 6 is a view for explaining a fifth embodiment.

DESCRIPTION OF EMBODIMENTS

However, in the above-discussed method where the conductive circuit isformed by the screen printing, in a case where the conductive materialused for the conductive paste is made of silver (Ag), while silver (Ag)has an electric resistance value of 5.0×10⁻⁵ [Ω·cm] and goodconductivity, silver may react with sulfur (S) so that silver sulfide isformed or migration may be generated. In a case where the conductivematerial used for the conductive paste is made of copper (Cu), copper(Cu) has an electric resistance value of 2.5×10⁻⁴ [Ω·cm] and theconductivity of copper (Cu) is lower than that of silver (Ag). In a casewhere the conductive material used for the conductive paste is made ofcarbon (C), while carbon does not react with sulfur (S) so thatsulfurization does not occur and migration is not generated, theconductive material has an electric resistance value of 3.0×10⁻² [Ω·cm]and the conductivity of carbon (C) is lower than that of copper (Cu).

In a case where a tin (Sn) group solder not including lead (Pb) is usedas a connecting material for connecting the interlayer of the circuitboard, the interlayer is connected at a temperature of 240° C. through260° C. which is higher than 221° C. being a melting point of a tin(Sn)-silver (Ag) alloy (217° C. being a melting point of a tin (Sn)-3silver (Ag)-0.5 copper (Cu) alloy). There is almost no connectingmaterial whose main ingredient is tin (Sn) and whose melting point isequal to or greater than 260° C. being a heat-resistant temperature ofthe circuit board. Therefore, for example, a material whose mainingredient is gold (Au) should be selected as the connecting materialfor connecting the interlayer of the circuit board.

However, an alloy group whose main ingredient is gold (Au) has a highmelting point. For example, a melting point of a gold (Au)-tin (Sn)alloy is 280° C. A melting point of a gold (Au)-tin (Sn) alloy is 280°C. A melting point of a gold (Au)-germanium (Ge) alloy is 356° C. Amelting point of a gold (Au)-silicon (Si) alloy is 370° C. Therefore, ina case where these materials are used as the connecting material forconnecting the interlayer of the circuit board, thermal damage appliedto other members forming the circuit may become large. In addition,since gold (Au) is a main ingredient of these materials, there may be aproblem of material cost. Furthermore, a material of an alloy groupwhose main ingredient is gold (Au), compared to a lead (Pb)-tin (Sn)group solder material, is solid and fragile, so there may be a problemin terms of connecting reliability.

In addition, due to heat applied when the electronic component isconnected to the circuit board and difference of coefficients of thermalexpansion between the electronic component and the circuit board, aposition shift of a minute connecting part of the electronic componentmay be a serious problem for connectability. Accordingly, it ispreferable that the heating temperature at the time of connecting belower. For example, in a case of an organic circuit board having a highcoefficient of thermal expansion, it is necessary to make the heatingtemperature be equal to or lower than 160° C. On the other hand, in acase where the connecting temperature is low, if the connecting part isremelted by other processes, reliability may be degraded. Therefore, itis necessary for a structure of the connecting part of the final productto bear the high temperature.

As a means for solving this problem, a nano paste material using nanosize particles has been recently developed. However, in the case of thenano paste material, while the nano paste material may be easilysintered (cohesive coupled) at a low temperature, the manufacturing costof the nano size particles is high because a manufacturing method of thenano-size particles is specific.

Preferred embodiments of the present disclosure will be explained withreference to accompanying drawings.

FIGS. 1( a)-1(c) are views for explaining embodiments.

As shown in FIG. 1( a), in a conductive material 10 of the embodiments,a second metal part 12 is formed on a surface of a first metal part 11as a core. The first metal part 11 is a particle of metal or alloy whosemain ingredient is a first metal. The second metal part 12 is an alloyfilm whose main ingredient is a second metal. The second metal has amelting point lower than the melting point of the first metal. Thesecond metal and the first metal can form an intermetallic compound. Inaddition, a third metal part 13 is mixed in the conductive material 10.The third metal part 13 is made of a powder of an alloy or a metal whosemain ingredient is a third metal. The third metal can undergo a eutecticreaction with the second metal.

As the first metal forming the first metal part 11, for example, copper(Cu) or an alloy of copper (Cu) such as a powder of brass or phosphorcopper can be used.

As the second metal forming the second metal part 12, tin (Sn) or analloy of tin (Sn) whose main ingredient is tin (Sn), such as tin(Sn)-silver (Ag), tin (Sn)-zinc (Zn), tin (Sn)-indium (In), tin(Sn)-antimony (Sb), or tin (Sn)-bismuth (Bi), can be used.

As the third metal forming the third metal part 13, a powder of bismuth(Bi), indium (In), or bismuth (Bi)-silver (Ag) or bismuth (Bi)-copper(Cu) whose main ingredient is bismuth (Bi) can be used.

Since the conductive material 10 can be used for forming a minutecircuit, embedding in vias, connecting an electronic component, or thelike, a grain size of the powder may be equal to or less thanapproximately 10 μm. Because of this, an electroless plating method maybe used for forming a film of the second metal forming the second metalpart 12 on the surface of the first metal forming the first metal part11. It is general practice that a barrel plating method usingelectroplating is used as a method for plating metal powder. However, ina case of a process for an impalpable powder using the barrel platingmethod, the yield rate may be decreased and it may be difficult tocontrol a film thickness of plating. Accordingly, the electrolessplating method for a material having the above-mentioned problem may beused.

A plating thickness of the film of the second metal by the electrolessplating method can be properly set by the grain size of the powder ofthe first metal, the grain size of the powder of the third metal, acompounding ratio, and others. From the view point of adhesion at a lowtemperature and high melting point, in order to make a diffusion processprogress, the plating thickness of the film of the second metal may beapproximately 1 μm through approximately 3 μm.

The compounding ratio of the powder of the first metal of the firstmetal part 11 having the surface on which the second metal part 12 isformed and the powder of the third metal forming the third metal part 13can be properly changed based on use. However, from the view point ofadhesion at a low temperature and high melting point, in order to make adiffusion process progress, the compounding ratio of the powder of thethird metal may be approximately 20% through approximately 60%.

In order to make the conductive material be in a paste state, from theview point of supplying the paste by printing, a ratio of the powder maybe approximately 70 wt % through approximately 95 wt %. In a case wherethe paste is supplied by using other methods such as a dispensing methodor an ink jet method, the ratio of the powder may be equal to or lessthan approximately 70 wt %.

When a heating process and a pressurization process are applied so thatthe temperature of the conductive material reaches a temperature equalto or lower than a heat resistant temperature of an insulation substrateused as the circuit board and equal to or lower than a glass transitiontemperature of the substrate (for example, equal to or lower thanapproximately 160° C.), an eutectic reaction of the second metal formingthe second metal part 12 and the third metal forming then third metalpart 13 is generated. As a result of this, as illustrated in FIG. 1( b),a metallic compound 14 of the second metal and the third metal is formedaround the first metal part 11.

When a heating process and a pressurization process are applied, asillustrated in FIG. 1( c), the first metal of the first metal part 11and the second metal in the metallic compound 14 react with each otherso that a metallic compound 15 of the first metal and the second metaland the third metal part 13 having melting points higher than the heatresistant temperature of the insulation substrate used as the circuitboard (for example, a temperature equal to or higher than 260° C.) areformed. The third metal part 13, as well as the metallic compound 15,also has a melting point higher than the heat resistant temperature ofthe insulation substrate used as the circuit board (for example, atemperature equal to or higher than 260° C.). Accordingly, theconductive material shown in FIG. 1( c) has an increased melting pointand therefore is not melted at a temperature higher than the heatresistant temperature of the insulation substrate used as the circuitboard (for example, a temperature equal to or higher than 260° C.).

A circuit part including the above-mentioned conductive material isthermally stable. The conductive material is not remelted atapproximately 220° C. through approximately 240° C. which is a reflowsoldering temperature in a case where the electronic component ismounted on the circuit board.

Such a conductive material can be used as a conductive paste where resincomponent is mixed. A resin component, where any of an epoxy group, aphenol group and a silicon group is used as a base and an organic acidor the like is added, can eliminate or prevent oxidization of theconductive material, so as to form a good-bonding metallic body. Forexample, a conductive paste as a connecting material, like a solderpaste, can be formed by mixing the conductive material, rosin resin, anorganic acid or a halogen group active ingredient, and a solvent.

In addition, the metallic compound 15 of the first metal and the secondmetal has an electric resistance value so that the metallic compound 15can be used as a conductive circuit of the circuit board. Hence, it ispossible to mount the electronic component on the circuit boardincluding the conductive circuit formed by the conductive material orthe conductive paste of the embodiments.

The above-mentioned conductive material and conductive paste can be usedas a connecting member of the electronic component such as asemiconductor element, since the above-discussed conductive material andconductive paste can be used in substitution for solder including lead(Pb) having a high melting point. Hence, it is possible to connect theelectronic component such as the Semiconductor Element to the Board at aLow temperature where there is little influence of the difference incoefficients of thermal expansion and then to form the connecting partwith high reliance where the melting point is increased.

[a] First Embodiment

Next, a first embodiment is discussed.

The inventors prepared seven kinds of conductive materials A through Gmentioned in a TABLE 1. More specifically, a copper (Cu) powder havinggrain size of approximately 5 μm through approximately 10 μm was used asthe first metal forming the first metal part 11 illustrated in FIG. 1.Conductive particles where a film having thickness of approximately 2 μmand made of electroless tin (Sn) plating, electroless tin (Sn)-silver(Ag) plating, or electroless tin (Sn)-indium (In) plating was formed onthe surface of the first metal as the second metal forming the secondmetal part 12, and a bismuth (Bi) powder, a bismuth (Bi)-silver (Ag)powder, or a bismuth (Bi)-copper (Cu) powder as the third metal formingthe third metal part 13 were mixed. Thereby seven kinds of theconductive materials A through G were formed.

A mixture ratio of the third metal forming the third metal part 13 tothe first metal forming the first metal part 11 having the surface wherethe second metal part 12 was formed could be properly selected in arange of approximately 20% through approximately 60% in order to achievelow temperature connecting and increase of the melting point. Themixture ratio of each of the conductive materials A through G isindicated in the following TABLE 1.

TABLE 1 Mixing Conductive Ratio of Material 1^(st) Metal 2^(nd) Metal3^(rd) Metal 3^(rd) Metal A Cu Electroless Bi 50% Powder Sn Powder B CuElectroless Bi 50% Powder SnAg Powder C Cu Electroless BiAg 60% PowderSn Powder D Cu Electroless BiAg 60% Powder SnAg Powder E Cu ElectrolessBiCu 40% Powder Sn Powder F Cu Electroless BiCu 40% Powder SnAg Powder GCu Electroless Bi 50% Powder SnIn Powder

In addition, by mixing each of the above-mentioned conductive materialsA through G and a resin ingredient where bisphenol F type epoxy resin, acuring agent, and adipic acid are mixed were mixed at 6:4, seven kindsof conductive pastes 1 through 7 were made. To each of the conductivepastes 1 through 7, a heating process at approximately 100° C. throughapproximately 290° C. was applied twice.

FIG. 2 is a graph of temperature change and a measuring result of aheating amount (heating rate) by two heating processes.

In the graph indicated in FIG. 2, the vertical axis represents theheating amount [μW] and the horizontal axis represents temperature [°C.]. In addition, a solid line indicates temperature change and ameasuring result of the heating amount by the first time heatingprocess. A one-dotted line indicates temperature change and a measuringresult of the heating amount by the second time heating process.

As illustrated in FIG. 2, it is found that, in any of the conductivepastes 1 through 7, by the first time heating process, at 137.9° C., aeutectic reaction between the second metal and the third metal isgenerated so that a metallic compound of the second metal and the thirdmetal is formed. It is also found that, at 198.9° C., the first metaland the second metal forming the metallic compound of the second metaland the third metal reacted with each other. By applying the second timeheating process after the first time heating process was completed, theeutectic reaction of the second metal and the third metal was notgenerated at 137.9° C. It was found that the heating amount is reducedwhen the temperature reached 271° C.

This phenomenon indicates that the melting points of the conductivepastes 1 through 7 are increased so as to reach a temperature higherthan the heat resistant temperature of the insulation substrate used asthe circuit board (for example, a temperature equal to or higher than260° C.).

The inventors confirmed the status of the conductive paste after theheating process. It was found that each of the conductive pastes 1through 7 is changed to a structure where the first metal part made ofcopper (Cu), the metallic compound of copper (Cu) and tin (Sn) formed onthe surface of the first metal part, and bismuth (Bi) formed on an uppersurface of the metallic compound are formed. In addition, the inventorsmeasured electric resistance of each of the conductive pastes 1 through7 after the heating process. It was found that the conductive pastes 1through 7 had respective low resistances between 1.0×10⁻⁶ Ω·cm and2.0×10⁻⁶ Ω·cm.

TABLE 2 Paste Resistance [Ω · cm] 1 1.5 × 10⁻⁶ 2 1.0 × 10⁻⁶ 3 1.5 × 10⁻⁶4 1.5 × 10⁻⁶ 5 1.3 × 10⁻⁶ 6 1.0 × 10⁻⁶ 7 2.0 × 10⁻⁶

The inventors also mixed the conductive materials A through G and aresin ingredient where rosin resin, acetic anhydride, and Butyl carbitolwere mixed at 9:1, so that seven kinds of conductive pastes 8 through 14were made. In addition, after a heating process at approximately 100° C.through approximately 290° C. is repeated twice for each of theconductive pastes 8 through 14, the electric resistance of each of theconductive pastes 8 through 14 was measured. As indicated in TABLE 3,the conductive pastes 8 through 14 have respective low resistancesbetween 5.0×10⁻⁶ Ω·cm and 6.0×10⁻⁶ Ω·cm.

TABLE 3 Paste Resistance [Ω · cm] 8 5.0 × 10⁻⁶ 9 5.0 × 10⁻⁶ 10 5.2 ×10⁻⁶ 11 5.5 × 10⁻⁶ 12 5.3 × 10⁻⁶ 13 5.0 × 10⁻⁶ 14 6.0 × 10⁻⁶

[b] Second Embodiment

The inventors, as illustrated in FIG. 3, supplied the above-discussedconductive pastes 1 through 7 (indicated by “P” in FIG. 3) in via holesformed in the wiring board (circuit board) 20. A base material of thewiring board (circuit board) 20 is insulation resin such as glass epoxyresin. Conductive patterns (wiring parts) 21 and 22 made of copper (Cu)or the like are selectively provided on upper and lower surfaces of thewiring board (circuit board) 20.

The via hole can be formed by a drilling process, laser processing, orthe like and has, for example, a diameter of approximately 100 μm. Anyof the above-mentioned conductive pastes 1 through 7 can be supplied inthe via holes by, for example, screen printing or the like. Any of thecured conductive pastes 1 through 7 can electrically connect theconductive patterns 21 and 22 formed on upper and lower surfaces of thebase material of the wiring board.

After applying the heating process at approximately 150° C. in a vacuumstate to such a structure, the inventors confirmed, as well as theresults provided in TABLE 2 and TABLE 3 of the first embodiment, theforming of a low resistance circuit. In addition, the remeltingphenomenon where the conductive pastes 1 through 7 supplied in the viaholes and cured was not observed even if heating at a temperature higherthan the heat resistant temperature of the insulation substrate used asthe circuit board (for example, a temperature equal to or higher than260° C.) was applied. A conductive connection through a via holestructure having high reliability could be formed.

[c] Third Embodiment

FIGS. 4( a) and 4(b) are views for explaining a third embodiment. FIG.4( b) is an expanded view of a portion surrounded by a dotted line inFIG. 4( a).

A multilayer wiring board 30 of this embodiment has a structure where aresin substrate 20 a and a resin substrate 20 b are stacked via anadhesive tape 35. A base material of the resin substrate 20 a is aninsulation resin such as glass epoxy resin. Conductive patterns (wiringparts) 21 made of copper (Cu) or the like are provided on an uppersurface and inside of the resin substrate 20 a. A base material of theresin substrate 20 b is an insulation resin such as glass epoxy resin.Conductive patterns (wiring parts) 22 made of copper (Cu) or the likeare provided on a lower surface and inside of the resin substrate 20 b.

The inventors formed the multilayer wiring board 30 by the followingmethod. Via holes are formed in positions of the adhesive sheet 35corresponding to the conductive patterns 21 formed inside the resinsubstrate 20 a and the conductive patterns 22 formed inside the resinsubstrate 20 b. Any of the above-discussed conductive pastes 1 through 7are supplied in the via holes. In FIG. 4, the conductive pastes 1through 7 are indicated by the reference “P”.

The via hole can be formed by a drilling process, a laser processing, orthe like and has, for example, a diameter of approximately 100 μm. Anyof the above-mentioned conductive pastes 1 through 7 can be supplied inthe via holes by, for example, screen printing or the like. Any of thecured conductive pastes 1 through 7 may electrically connect theconductive patterns 21 and 22 formed inside the resin substrates 20 aand 20 b.

After applying the heating process at approximately 150° C. in a vacuumstate to such a structure, the inventors confirmed, as well as theresults provided in TABLE 2 and TABLE 3 of the first embodiment, theforming of low resistance circuits. In addition, the remeltingphenomenon where the conductive pastes 1 through 7 supplied in the viaholes and cured was not observed even if heating at a temperature higherthan the heat resistant temperature of the insulation substrate used asthe circuit board (for example, a temperature equal to or higher than260° C.) was applied. A multi-layer wiring board including a conductiveconnection through a via hole structure having high reliability could beformed.

[d] Fourth Embodiment

FIG. 5 is a view for explaining a semiconductor device 40 of a fourthembodiment.

In forming the semiconductor device 40, convex-shaped (projecting)outside connection terminals 44 formed on a main surface of asemiconductor element 43 are connected to electrode terminals 42 exposedon an upper surface of a wiring board (circuit board) 41. In otherwords, the semiconductor element 43 is mounted on the wiring board 41 ina so-called flip chip (face down) state. The wiring board 41 has a basemember made of insulation resin such as glass epoxy resin manufacturedby a built-up process. The electrode terminals 42 are made of copper(Cu). A base material of the semiconductor element 43 is silicon (Si) orthe like.

More specifically, the convex-shaped (projecting) outside connectionterminals 44 called bumps are formed, by gold (Au) plating, on electrodepads (not illustrated in FIG. 5) formed on, with approximately 80 μmpitches, a main surface of the semiconductor element 43 having asubstantially square shaped configuration whose one side has a length ofapproximately 10 mm. Then, any of the conductive pastes 8 through 14discussed with reference to TABLE 3 (illustrated by the reference “P′”in FIG. 5) are transferred to the electrode terminals 42 of the wiringboard 41. After that, the convex-shaped outside connection terminals 44and the electrode terminals 42 of the wiring board 41 are positioned andconnected to each other and a heating process at approximately 150° C.is applied.

After that, an underfill agent is supplied by capillary reflow betweenthe wiring board 41 and the semiconductor element 43 and a curingprocess at approximately 180° C. is applied for approximately one hour.As a result of this, a connection resistance at a connection portionwhere any of the conductive pastes 8 through 14 are used isapproximately 5.0×10⁻⁶ Ω·cm. Hence, it could be confirmed that theconnection resistance of this embodiment, as well as that in the firstembodiment, was low and a good connecting part was formed. It was alsoconfirmed that this connecting part was not remelted at a temperaturelower than the heat-resistant temperature of the wiring board 31 such asa temperature equal to or lower than approximately 260° C.

[e] Fifth Embodiment

FIG. 6 is a view for explaining a semiconductor device 50 of a fifthembodiment.

In forming the semiconductor device 50, convex-shaped (projecting)outside connection terminals 45 formed on a main surface of asemiconductor element 43 are connected to electrode terminals 42 exposedon an upper surface of a wiring board (circuit board) 41. In otherwords, the semiconductor element 43 is mounted on the wiring board 41 ina so-called flip chip (face down) state. The wiring board 41 has a basemember made of insulation resin such as glass epoxy resin manufacturedby a built-up process. The electrode terminals 42 are made of copper(Cu). A base material of the semiconductor element 43 is silicon (Si) orthe like.

More specifically, the conductive paste 8 discussed with reference toTABLE 3 is printed on the electrode terminals 42 formed on, withapproximately 150 μm pitches, a main surface of the wiring board 41having a substantially square shaped configuration whose one side has alength of approximately 10 mm. A heating process at approximately 150°C. was applied so that the convex-shaped (projecting) outside connectionterminals 45 called bumps are formed. On the other hand, the conductivepastes 8 are printed on the electrode terminals 42 of the wiring board41.

After that, the outside connection terminals 45 and the electrodeterminals 42 of the wiring board 41 were positioned so as to beconnected to each other and then a heating process at approximately 150°C. was applied.

Then, an underfill agent was supplied by capillary reflow between thewiring board 41 and the semiconductor element 43 and a curing process atapproximately 180° C. was applied for approximately one hour. As aresult of this, a connection resistance at a connection portion wherethe conductive paste 8 is used is approximately 5.0×10⁻⁶ Ω·cm. Hence, itcould be confirmed that the connection resistance of this embodiment, aswell as that in the first embodiment, was low and a good connecting partwas formed. It was also confirmed that this connecting part was notremelted at a temperature lower than the heat-resistant temperature ofthe wiring board 41 such as a temperature equal to or lower thanapproximately 260° C.

As discussed in the first through fifth embodiments, according to theconductive material of the embodiments, an electric connecting part isformed by the metallic compound and the third metal being the mainingredient of the third metal part. The metallic compound is formed bythe first metal being the main ingredient of the first metal part andthe second metal being the main ingredient of the second metal part.

According to the embodiments, it is possible to provide a conductivematerial having an electric resistance value lower than that of therelated art conductive material, which conductive material can be meltedand connected at a temperature equal to or lower than the heat-resistanttemperature of the insulation substrate used as the circuit board. Theconductive material has a melting point higher than the heat-resistanttemperature of the insulation substrate due to the metallic reaction andcan endure heat at a soldering temperature of the electronic component.In addition, it is possible to realize an electric connection havinghigh reliability and sufficient strength.

In addition, the conductive material of the embodiments has a meltingpoint higher than the heat-resistant temperature of the insulationsubstrate. Therefore, it is possible to form the circuit and connect theelectronic component at a low temperature. Hence, it is possible toreduce the stress which may be generated in a manufacturing process ofthe circuit board and the semiconductor device.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority orinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

The above-discussed embodiments can be applied to the conductivematerial and the conductive paste which is used for forming theconductive circuit in and on the circuit board and making interlayerconnection between the circuits. The above-discussed embodiments can beapplied to the circuit board and the semiconductor device using theconductive material or the conductive paste.

What is claimed is:
 1. A circuit board, comprising: a plurality ofcircuit parts; a connecting part including conductive material,comprising: a first metal part whose main ingredient is a first metal; asecond metal part formed on the first metal part and whose mainingredient is a second metal, the second metal having a melting pointlower than a melting point of the first metal, which second metal canform a metallic compound with the first metal; and a third metal partwhose main ingredient is a third metal, which third metal can make aeutectic reaction with the second metal; wherein the circuit parts areconnected to each other by the connecting part.
 2. The circuit board asclaimed in claim 1, wherein the connecting part is formed of themetallic compound and the third metal, which metallic compound is formedby the first metal being the main ingredient of the first metal part andthe second metal being the main ingredient of the second metal part, thethird metal being the main ingredient of the third metal part.
 3. Thecircuit board as claimed in claim 1, wherein the circuit board is amulti-layer wiring board where a plurality of resin substrates havingthe circuit parts is stacked.
 4. A semiconductor device, comprising: asemiconductor element; and a wiring board having a main surface wherethe semiconductor element is connected, wherein the wiring board is thecircuit board as claimed in claim
 1. 5. A semiconductor device,comprising: a semiconductor element; and a wiring board having a mainsurface where the semiconductor element is connected, wherein the wiringboard and the semiconductor element are connected to each other by aconnecting part including a conductive material comprising a first metalpart whose main ingredient is a first metal; a second metal part formedon the first metal part and whose main ingredient is a second metal, thesecond metal having a melting point lower than a melting point of thefirst metal, which second metal can form a metallic compound with thefirst metal; and a third metal part whose main ingredient is a thirdmetal, which third metal can make a eutectic reaction with the secondmetal.
 6. The semiconductor device as claimed in claim 5, wherein theconnecting part is formed of the metallic compound and the third metal,which metallic compound is formed of the first metal being the mainingredient of the first metal part and the second metal being the mainingredient of the second metal part, the third metal being the mainingredient of the third metal part.
 7. A conductive material,comprising: a first metal part whose main ingredient is a first metal; asecond metal part formed on the first metal part and whose mainingredient is a second metal, the second metal having a melting pointlower than a melting point of the first metal, which second metal canform a metallic compound with the first metal; and a third metal partwhose main ingredient is a third metal, which third metal can make aeutectic reaction with the second metal.